fgraph: Allocate ret_stack_list with proper size

From: Steven Rostedt <[email protected]>

The ret_stack_list is an array of ret_stack shadow stacks for the function graph usage. When the first function graph is enabled, all tasks in the system get a shadow stack. The ret_stack_list is a 32 element array of pointers to these shadow stacks. It allocates the shadow stack in batches (32 stacks at a time), assigns them to running tasks, and continues until all tasks are covered.

When the function graph shadow stack changed from an array of ftrace_ret_stack structures to an array of longs, the allocation of ret_stack_list went from allocating an array of 32 elements to just a block defined by SHADOW_STACK_SIZE. Luckily, that's defined as PAGE_SIZE and is much more than enough to hold 32 pointers. But it is way overkill for the amount needed to allocate.

Change the allocation of ret_stack_list back to a kcalloc() of FTRACE_RETSTACK_ALLOC_SIZE pointers.

Fixes 42675b723b484 ("function_graph: Convert ret_stack to a series of longs")

Signed-off-by Steven Rostedt (Google) <[email protected]>

---
 kernel/trace/fgraph.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

kernel/trace/fgraph.c +2 -1

index 43f4e3f57438..41e7a15dcb50 100644
@@ -1162,7 +1162,8 @@ static int start_graph_tracing(void)
 	unsigned long **ret_stack_list;
 	int ret;
 
-	ret_stack_list = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
+	ret_stack_list = kcalloc(FTRACE_RETSTACK_ALLOC_SIZE,
+				 sizeof(*ret_stack_list), GFP_KERNEL);
 
 	if (!ret_stack_list)
 		return -ENOMEM;

Signature · 1 line

2.45.2